Our statistics draw that the average chemistry student has not done laboratory experiments within the last five years. In this exercise, we will carry out simple kitchen chemistry experiments that will allow you to sharpen your observational skills and get some quick feedback on your laboratory report writing skills. Remember you do not need your all-home microlab kit to do any of these experiments.

Introduction

In the winter of 1859, Michael Faraday, a famous English scientist (see p. 827, Jones and Atkins, Molecules, Matter and Change, 4th ed.), gave several lectures centered around the chemistry and physics of a candle! Faraday would tell his listeners:

There is not a law under which any part of this universe is governed which does not come into play and is touched upon in these phenomena. There is no better, there is no more open door by which you can enter into the study of natural philosophy than by considering the phenomena of a candle.

He would then proceed and set out to prove his point by lighting a candle and demonstrating all the processes involved. We will enter the lab portion of Chemistry 217 by that same door and will repeat some of the experiments that Mr. Faraday demonstrated more than a century ago. In so doing, we hope you will exercise your power of observation and sharpen some of your experimental skills to help prepare you for the more concentrated in-lab experiments you will be challenged with later on.

In burning a candle one starts with a solid fuel (wax), which is liquified, rising up into the wick by capillary action to be vapourized in the atmosphere, and then quickly oxidized by the candle flame. In burning, the candle produces energy in the form of heat and light. The burning process is a simple organic chemical reaction represented by the following equation:

If one were to remove the fuel (wax), the oxygen or the initiator (flame) or any combination of the three, the candle would go out. Professional fire-fighters use this idea constantly when they develop strategies for fighting fires.

Figure CE.1
Candle flame

Figure CE.1 shows a detailed diagram of the flame of a burning candle and will give you a better idea of the mechanics involved.

Procedure

A. Re-igniting a Candle

Light a candle and let it burn for about one minute.

Have a lighted match or lighter ready.

Carefully blow out the candle.

Watch the smoke trail coming up from the extinguished candle and quickly place your lighted match into that smoke stream.

The candle should re-ignite.

B. Water Suck Up

With a few drops of hot wax fix your candle to the center of a bowl.

Pour water into the bowl so that it is partially filled.

Light the candle.

Place an empty jar or glass over the candle so that the edge is under the water line (see Figure CE.2).

The candle should extinguish.

Figure CE.2
Candle under glass

C. Extinguishing a Candle with Aluminum Foil

Mold and cut a square of aluminum foil into the shape shown in Figure CE.3.

Place the foil between the candle and flame so that the wick goes through the slit in the foil.

The candle should extinguish (the slit may have to be narrowed manually).

Figure CE.3
Aluminum foil

D. Candle Condensation

Place several ice cubes into a large square of aluminum foil.

Pull together the corners to form a sack filled with ice.

Hold this sack over (about 20 cm) a burning candle.

Water droplets should form on the outside of the aluminum sack.

E. Extinguishing a Candle with Carbon Dioxide

Fix a candle in a glass jar and light it.

In the another glass jar add two tablespoons of baking soda.

Then add about 1/5 cup of vinegar to the baking soda.

The baking soda will foam.

Quickly tip the foaming glass and “pour” the carbon dioxide formed into the jar with the burning candle.
Note: Be careful not to tip the wet vinegar/baking soda mixture into the candle jar.

The candle should extinguish.

Observations and ResultsNote that formally observations and results or explanations for the observations are treated separately in a laboratory report. Since these experiments are rather simple, we will note our observations and
possible explanations for those observations in tabular form. You can
then incorporate this table into the short-report format described in the “Writing Laboratory Reports” section of this manual.

Experiment

Observations

Results and Explanations

A. Reigniting a Candle

B. Water Suck Up

C. Extinguishing a Candle with Aluminum Foil

D. Candle Condensation

E. Extinguishing a Candle with Carbon Dioxide

Questions

1.

Why did the candle reignite with a match held away from the wick?

2.

a.

Explain how the candle was extinguished with aluminum foil and carbon dioxide.

b.

Suggest and explain another method to extinguish a candle not already used in Part A of this experiment.

c.

Write out the balanced chemical equation for the reaction that produced carbon dioxide in this experiment.

3.

What does the formation of water on the aluminum ice sack suggest about the chemistry of a burning candle?

4.

a.

Suggest a reason why the water is sucked up into the glass jar.

b.

A candle flame will use up oxygen as it burns. However, the consumption of oxygen alone does not explain the observed volume change. What other factor(s) need to be considered?

5.

Explain the difference in the shapes of the two flames shown on page 53 of this manual.